Rotary shaft seals have been utilized in machinery, the automobile industry, as well as other industries. The seal has an air side and a lubricant side. The seal helps to maintain the lubricant (e.g. oil) on the lubricant side. Lubricant may, however, leak from the lubricated side to the non-lubricated (air) side through the interaction of the active surface of the seal with the shaft. Various arrangements have been devised to capture the leaked lubricant and deliver it back to the sealed side. In one, spiral grooves or built-up ribs (hereinafter collectively referred to as grooves) disposed on the active side of the seal capture the leaked lubricant and hydrodynamically pump the lubricant back into the lubricated side due to relative rotation between the seal and the shaft about which the seal is disposed.
The grooves used to hydrodynamically pump the lubricant are open at the oil side of the seal and communicate with the lubricant therein. Having the grooves open at the oil side of the seal creates potential problems. For example, static oil leaks can develop. Additionally, air leakage during pressurization testing of the machinery on which the seal is being used at the end of the assembly stage can also occur. In an attempt to address these drawbacks, the exit points of the spiral grooves on the oil side have been blocked. Blocking the exit point on the oil side, however, reduces the pump rate so significantly that the seal performance degrades and makes the use of such a seal impractical and/or impossible. Another attempt to address these drawbacks is to block the pumping groove not at the exit point on the inner side, but 2 to 3 loops of the groove toward the air side. Doing so reduces the pump rate also, but not to the extent where the seal performance degrades too much. This blockage, however, does lead to other difficulties. The most pronounced difficulty is oil stagnation close to the exit point. This in turn leads to oil coking in the groove and eventually to seal failure. Accordingly, it would be advantageous to provide a seal that effectively uses grooves to hydrodynamically pump lubricant back to the lubricant side while minimizing and/or eliminating the drawbacks mentioned above.
The seal with a controllable pump rate according to the principle of the present invention advantageously utilizes a groove on the active side or surface of the seal to capture leaked lubricant and hydrodynamically pump the lubricant back into the lubricated side. The groove extends along a portion of the active side of the seal. The groove, however, does not extend to the leading edge of the seal that faces the lubricant side. Rather, the groove stops short of the leading edge thereby forming a static dam or band between the groove and the sealing edge on the lubricant side of the seal. Lubricant that leaks past the sealing edge on the lubricant side is captured in the grooves and directed back toward the lubricant side due to relative rotation between the seal and the shaft on which the seal is disposed. The fluid pressure inside the groove grows until it reaches a critical value wherein the fluid pressure in the groove exceeds the seal lip opening pressure and the lubricant then escapes into the lubricant side of the seal. In some embodiments, the configuration of the groove is such that an induction zone is formed by a portion of the grooves and a booster zone is formed by a different portion of the grooves. The booster zone is adjacent the static dam. The fluid pressure growth is relatively slow in the induction zone and becomes relatively fast in the booster zone.
The use of a static dam in the seal of the present invention advantageously avoids static leakage and problems associated with insufficient fluid flow (coking, carbonization, etc.). Another advantage of the present invention is that some amount of lubricant is always present in the groove prior to the static dam liftoff. This lubricant provides improved seal lip lubrication thereby reducing wear and effectively removing coked lubricant and debris which in turn can extend the seal life.
In one aspect of the present invention, a dynamic seal includes a lubricant side and a non-lubricant side. A sealing portion is operable to engage with and seal against a shaft. The sealing portion includes an active surface communicating with the non-lubricant side and a seal lip at an end thereof. The seal lip faces the lubricant side and defines an opening in which a shaft can be disposed. The active surface is operable to engage with and seal against a shaft disposed in the opening. There is at least one pumping element extending along the active surface and stopping short of the seal lip. The pumping element has a beginning point and a termination point. The pumping element is operable to capture lubricant that leaks past the seal lip and pump the lubricant toward the termination point and back into the lubricant side due to relative rotation between the active surface and a shaft.
In another aspect of the present invention, another dynamic seal is disclosed. The dynamic seal has both a lubricant side and a non-lubricant side. An active surface is operable to seal against a shaft. At least one groove extends along the active surface from the non-lubricant side toward the lubricant side with a portion of the active surface disposed between the groove and the lubricant side. The groove is operable to capture lubricant that leaks between the active surface and the shaft and pump captured lubricant into the lubricant side past the portion of the active surface. A first portion of the groove has a first characteristic. A second portion of the groove has a second characteristic different than the first characteristic. The second portion of the groove is closer to the lubricant side than the first portion of the groove.
In still another aspect of the present invention, a method of returning lubricant that leaks past a dynamic seal on a shaft back to a lubricant side of the seal is disclosed. The method includes: (1) capturing lubricant that leaks past the seal in a groove on an active surface of the seal, the groove stopping short of the lubricant side of the seal; (2) pumping the captured lubricant in the groove back toward the lubricant side of the seal; (3) increasing a fluid pressure in the groove as the groove approaches the lubricant side of the seal; (4) lifting a portion of the seal adjacent the lubricant side off of the shaft with the fluid pressure in the groove; and (5) returning captured lubricant in the groove back to the lubricant side of the seal through a gap between the lifted-off portion of the seal and the shaft.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.